1. Field Of The Invention
The present invention generally relates to an automatic lateral guidance control system for controlling the direction of a moving vehicle, and more particularly, to an improved vehicle controller for use in an automatic lateral guidance control system for controlling the direction of a motor vehicle on a highway. So-called "Automated Highways" are presently being contemplated, which will include vehicular-based systems that will automatically control the motor vehicle's speed, steering and braking, in order to substitute for the driver as a prime source of control over the vehicle. The expected advantages of such systems will be to improve the overall flow of traffic and increase highway safety. The present invention is directed to such a vehicular-based system for automatically controlling vehicle direction.
2. Description of the Prior Art
A variety of conventional guidance systems are used for controlling the movement of vehicles travelling along a predetermined path, for example, as is illustrated in U.S. Pat. No. 4,049,961 to Marcy. Marcy discloses an automatic guidance system for a motor vehicle which includes an optical laser transmitter/receiver assembly. A series of spaced-apart responders (i.e., light reflective devices) are disposed in a single row parallel to the centerline of the roadway, or in a pair of rows on opposite sides of the centerline, for reflecting radiant energy from the laser transmitter back to the receiver. As shown in Marcy, the laser transmitter radiates two overlapping beams which are amplitude-modulated by sine waves that are 180 degrees out of phase. The receiver merges the two reflected beams into a single beam that is subject to a eyelid translatory shift in amplitude. The amplitude shift is translated into a voltage whose amplitude varies in accordance with the position or the vehicle. In other words, a comparison of the phase differences between the transmitted and reflected beams provides a determination of the vehicle's location with respect to the reflectors.
Stability augmentation systems which provide adaptive steering or correction for understeering or oversteering by comparing a desired vehicle steering condition with an actual vehicle steering condition, and correcting the steering angle of the steered wheels until the actual steering condition equals the desired steering condition are known. In such systems, both the vehicle speed and the steering wheel input angle, .delta..sub.sw, are converted by a microcontroller into a desired yaw rate .phi..sub.d '. The actual yaw rate .phi..sub.a ' is either measured directly or may be calculated. The controller then compares the actual and desired yaw rates, and corrects the angle of the steerable wheels independently of the steering input at the steering wheel until the actual and desired yaw rates are equal.